There is increasing concern about particulate matter (PM) emissions from gasoline engine vehicles. The concern is driven by the substantially higher emissions of small particulates from spark ignited gasoline powered vehicles that use direct injection (DI) of gasoline into at least one of the engine cylinders as a liquid. These small particulates lodge in the lungs and can be injurious to human health.
Although direct injection increases engine efficiency and performance by increasing knock resistance though evaporative cooling, use of DI throughout a drive cycle substantially increases the particulate emissions. Relative to conventional port fuel injected (PFI) engines, the particle number when operating with direct injection increases by factors of 10-100 over a drive cycle, depending on the cycle and the engine operating conditions. The emissions are especially concerning for engines that are turbocharged and this would also be the case for supercharged engines.
More stringent regulations on PM 2.5 (particulate matter less than 2.5 microns in diameter) are planned for Europe and anticipated in the US, including both EPA and California regulations. The European regulations would apply to the number of particulates as well as to the amount of particulate mass that is emitted.
Therefore, techniques that improve engine performance while minimizing particulate emissions would be beneficial.